35mm Film cameras

by Chris Woodford. Last updated: December 25, 2011.

Snap a photo with your camera, cellphone, or MP3 player and you have a piece of digital information you can use in all kinds of different ways: you can instantly email it to a friend, upload it to a website, or edit it on your computer. Only a few years ago, this sort of thing wasn't possible because cameras worked differently: they were entirely analog, capturing pictures as patterns of light and dark using chemically treated reels of plastic film, and a photograph took hours (or even days) to appear in your hand. Although some professional photographers still use film cameras, most of us have long since abandoned them to history, along with steam engines and the telegraph. That's a shame, because they can actually teach us quite a bit about chemistry, physics, and the science of light. Let's take a closer look at how they worked!

Photo: A typical 35mm film camera dating from the mid-1990s. This one's made by Olympus and includes a motorized zoom lens that extends up to 80mm. The plastic window at the top houses the autofocus system and the viewfinder and the white rectangle on the right (as we look at the camera) is the flash.

What is photography?

Articles like this typically open by noting that the word photography comes from two Greek words, photos (light) and graphos (writing)—so photography effectively means "writing with light." But that's just a metaphor. We see objects because they either emit light (like the Sun) or reflect it off their surface (like the Moon) in rays that zoom into our eyes in perfectly straight lines. Much like the human eye, a camera captures rays of light charging in through a lens at the front. But the crucial difference between a camera and your eye is that a camera makes a permanent copy of what it sees.

Photo: Photography is all about capturing light rays. Photo taken from the Space Shuttle by courtesy of NASA Johnson Space Center: Earth Sciences and Image Analysis (NASA-JSC-ES&IA).

"Photography" is a bit of a misnomer: it's not really true to say that light rays "write" or "draw" in any sense. They don't move back and forth, thoughtfully scribbling out a picture like an artist's hand. So what does happen? It always helps to think like a scientist! Remember that light is a form of energy; what a camera actually does is permanently capture the energy falling on a small, (two-dimensional) surface inside it. In a digital camera, that happens because there's an electronic light-detector chip called a CCD (charge-coupled device) immediately behind the lens, which converts the light energy into electricity. In a traditional camera, there's no CCD; instead, the incoming energy is captured by a piece of plastic that is sensitive to light, better known as the film. The light energy leaves a permanent trace by causing a chemical and physical transformation of the film. (Incidentally, light doesn't just mean visible light: you can, in theory, make a photograph from any kind of incoming light: infrared, ultraviolet x-ray, or whatever you wish.)

How does a film camera work?

The key features of a film camera are:

• A plastic or metal case that is completely light-tight to protect the film.
• An aperture (or diaphragm): a small circular hole in the case that lets in light for the short period when you want to take a photo.
• A shutter mechanism: a spring-loaded set of overlapping blades, like the ones you see at the start of a James Bond film, that open to let light in through the aperture for a precise amount of time before closing up again.
• One or more lenses in front of the shutter. The lenses are a crucial part of the camera and do several jobs at once. First, they scale down the large, incoming image of the world so it fits into a much smaller area of film: no-one really wants life-sized photos! Second, lenses concentrate the incoming light energy so the image forms on the film more quickly and the camera can be used in darker conditions than would otherwise be the case. Third, they bring the light rays into a sharp focus exactly on the surface of the film, so you get a clear, sharp, image rather than a blurred, fuzzy impression. Finally, they also minimize the distance between the aperture and the film so cameras can be made relatively small and portable. When you adjust the focus on a camera, you're actually moving one or more of the lenses back and forth (closer to or further from the object and the film) to make different parts of a scene appear sharper on the film, according to whether you want to emphasize near or distant objects in your photograph.
• A roll or piece of film (on the back wall of the camera directly opposite the shutter).

Photo: You can't easily open up a digital camera to see how it works, and even if you do, you don't learn that much. But film cameras reveal their secrets more freely. Open the back and you can see the spools (left and right) where the film goes. In the middle, you can see the back of the shutter mechanism and the lens in front of it. The viewfinder is the little clear plastic window at the top.

How to take a photo with a film camera

Photo: Taking a photo: freezing a moment of light forever. Picture by Victor Egorov courtesy of US Army.

When you're ready to take a photo, you point the camera at your subject, click a button, and the shutter opens briefly, allowing light rays to pass through the aperture and strike the film, usually for a fraction of a second before it closes up again. The incoming light rays cross over as they enter, with rays from the top of the object ending up on the bottom of the film and vice-versa, thus producing an upside-down (inverted) image on the film.

Film is very sensitive to light: only a tiny amount of light energy is needed to make a photograph and too much light will destroy it. To produce a perfect photo, you have to let exactly the right amount of light hit the film, which is called the exposure. The exposure depends on two factors: how long the shutter is open (the shutter speed) and how widely it's open (the aperture). Shutter speed is measured in seconds (anything from about 1/10,000 second to 30 seconds); aperture is measured in units called f-stops (or just "stops" for short), such as f/4 and f/8, with higher f numbers meaning more light is let in.

Automatic, compact, "point-and-shoot" cameras produce a reasonable image with the click of a single button: they use photocells (electronic light sensors) to automatically adjust the shutter speed and aperture and fire out invisible infrared or ultrasound beams to set the focus automatically as well. Although sophisticated professional cameras often have automatic controls, they also allow completely manual operation: before you can take a photo, you have to adjust the focus, set the exposure time, and adjust the size of the aperture. With manual cameras, you have to adjust the exposure time and aperture setting to compensate for one another, because both of them affect the amount of light reaching the film.

Other features

Most film cameras also have a viewfinder (so you can see how your photograph will appear), a xenon flash lamp (which adds enough extra light energy to activate the film, even in dark conditions), and self-timer mechanism (so you can photograph yourself without anyone's help). Inexpensive cameras generally have a viewfinder mounted to one side and above the main lens, so the image you compose is only an approximation of what you'll see on the final photograph. Professional cameras use a system called SLR (single lens reflex), in which prisms and mirrors allow you to look through the actual lens of the camera and see an exact replica of the photo you'll take. Most digital cameras (even inexpensive ones) produce a faithful copy of the final image, like SLRs, because the image you see on the LCD screen at the back is produced by the CCD that captures the final photograph.

While inexpensive point-and-shoot cameras generally have fixed lenses, professional SLRs are designed so you can unscrew one lens and screw in longer or shorter ones, as necessary, according to what you want to photograph. Lenses generally range from about 20mm (~0.8 inch) wide-angle lenses (for photographing something relatively wide and quite close) to 800mm (30 inches) or so ("elephant gun", telephoto lenses for taking very distant shots of quite narrowly defined areas). In between these two extremes, a typical everyday lens is about 50mm (2 inches) long. Many modern cameras have zoom lenses, usually powered by small electric motors, that can be moved back and forth between two fixed points to provide a whole range of different magnifications.

Photo: Need to take a photo at long range? Try a telephoto lens like this one, which is 400mm (~15 inches) long! Photo by Angela M. Virnig courtesy of US Navy.

How does photographic film work?

Many materials are sensitive to light. Leave a piece of white office paper in your window for a few weeks and you might well find it turns yellow; plastics that start off white or clear also have a habit of turning yellow or going foggy ("photodegrading") when they've been exposed to light for a while. The dyed colors in cotton clothes and fabrics will also fade in sunlight. And if you're Caucasian, even your skin may change color after a few hours or days on the beach. But you can't really use paper, plastic, cotton, or skin to capture a picture!

Photographic film is plastic (or sometimes paper) that's coated with an emulsion made from microscopically tiny crystals of silver salts suspended in gelatin (a jelly-like substance found in sweets such as wine gums). The silver salts are compounds of silver and halogens such as chlorine, iodine, and bromine, also called silver halides—and their useful feature is the way they begin to change into pure, metallic silver when light falls onto them. If lots of light hits them, they change much more dramatically than if less light hits. This is how the two-dimensional pattern of light rays entering through the lens of a camera from the world outside forms a kind of invisible, chemical trace (called a "latent" image) on the surface of photographic film.

Developing and printing photographic film

Photo: A photographic darkroom is usually lit with dim green or red light to prevent damage to undeveloped film. Photo by Leah Stiles courtesy of US Navy.

A light-sensitive slice of plastic film with an image invisibly imprinted on it isn't much use to anyone. To turn it into a recognizable photo, you have to develop the film in a darkroom (usually lit with red or green light that doesn't affect the film). This involves dipping the film in a series of chemicals, which convert the latent image captured by the tiny silver halide crystals into a visible image formed of larger silver particles, and also makes that image permanent.

First, the film is dipped in an acidic solution called developer, which encourages more of the silver halide to convert to metallic silver and renders the latent image visible. To stop this process continuing indefinitely, and ruining the photo, the film then has to be dipped in an acidic solution called a stop bath to neutralize the developer. Once that's done, the image is made permanent by dissolving any remaining silver halide using a chemical solution known as hypo (or fixer), before being rinsed clean in water and hung up to dry.

At this stage, the image, though visible, is still in a negative pattern, with light areas looking dark and vice versa. That's why developed pieces of film are called negatives. Once the film is developed, it's printed: broadly speaking, you shine a light through the negative so it casts a shadow onto photo-sensitive paper and turns the negative film into a recognizable photograph called a (positive) print. You can make any number of prints from a single negative, which is one of the great advantages of this slightly laborious, "positive-negative" photographic process. By adjusting the distance between the negative and the paper you're printing on, and using lenses, you can also enlarge or reduce the size of a an image. The piece of equipment you use to do this is called an enlarger.

Artwork: The photographic process captures an image as a photograph in three main steps. 1: Exposure captures an inverted (upside down) latent (invisible) image on the film inside your camera. 2: Developing uses a series of chemicals to make the latent image visible and fix it permanently on the film in the form of a negative. 3: Printing produces a final photograph (a positive print) from the negative. You can make any number of prints from one negative.

It's possible to develop and print films yourself, but most photographic laboratories have large electronic machines that automate the process completely, threading the film through a series of tanks filled with chemicals in the correct sequence, at just the right speed. Those big photo-printing machines you still sometimes see in the back of drug stores typically use a method of developing color film called the C-41 process.

Photo: Left: A photographic color negative of some recycling dumpsters looks like this. Right: When it's printed, the colors are reversed and come out looking as you'd expect. I've simulated the effect of printing by reversing the colors digitally with a computer graphics package. Notice how the real-life red dumpster (in the center in the positive image on the right) turns green in the negative, while the yellow one (on the right in the positive image) turns blue in the negative.

Types of film

Most film is sold in light-tight cartridges that you snap into your camera. Inside, the cartridges contain a long reel of plastic film separated into one, two, or three dozen rectangular frames that measure 24mm x 36mm (this standard size is called 35mm film). The top and bottom of the reel is punched with little holes so each section of the film can be wound out of the way after a photo is taken, releasing an unexposed frame ready for the next photo. (Cameras generally have either a spool mechanism slowly wound by hand or automatically and very quickly wound by an electric motor.)

Photo: A typical piece of 35mm color photographic film. You can just about make out that there are four frames here, side by side. So a roll of film with 36 frames on it would be about nine times this length. Note the sprocket holes at the top and bottom for winding the film accurately through the camera.

There are numerous different kinds of film designed for taking different kinds of photo. Black and white film is sensitive only to the presence or absence of light, so it shows images only as shades of gray. Color film effectively works the same way as black and white only with three separate layers, one sensitive to blue, one sensitive to green, and one sensitive to red light. Films are also designed to work in widely different light conditions: generally speaking, you need to use a fast film (one that forms an image with relatively little light) in dark, indoor conditions and a slow film (one that needs more light) in bright, outdoor conditions. The film speed is indicated by a number called the ISO rating: ISO numbers of 100 are slow, 400 or more are fast, and 200 are good for general-purpose photography. Fast films generally produce grainier, more blurry images than slow ones so, as a rule, photographers never use a faster film than is absolutely necessary. Modern cameras automatically detect film speed using a system called DX coding, which simply involves the camera reading a barcode printed on the film container. For no real reason other than convention, good digital cameras also tend to use ISO ratings to indicate how quickly photographs are taken in different light conditions.

A brief history of photography

Who invented cameras? Here's a brief history of the key moments in the development of film-based photography:

• Ancient times: People figure out how to produce images on the walls of darkened rooms by making holes in the shutters or drapes on an opposite wall. This is called a camera obscura.
• 1727: German physicist Johann Schulze discovers the essential piece of science that will underpin all photography until the late 20th century: silver-based chemical salts are sensitive to light.
• Late 18th century: Sir Humphry Davy and Thomas Wedgwood use silver-coated paper to make crude copies of paintings.
• 1827: Frenchman Joseph Nicéphore Niépce makes the first photograph, a view from his window, using a metal plate coated with silver chemicals exposed to the light for eight-hours.
• 1831: With Niépce's help, another Frenchman, Louis Daguerre (pictured, right), perfects a method of making extremely detailed photographic images on silver plates, named daguerreotypes. The method becomes hugely popular in the United States. Photo of Louis Daguerre courtesy of US Library of Congress.
• 1839: Henry William Fox Talbot figures out how to make photographs on light-sensitive paper coated with silver-based chemicals. He invents the negative-positive process and the way of making multiple prints from a single negative. His pictures are initially called Talbotypes or Calotypes until a friend of his, English astronomer Sir John Herschel, suggests "photographs" might be a better name.
• 1851: English artist Frederick Scott Archer invents a new way of making photographs using wet glass plates. Although cheaper than daguerreotypes and better quality than Fox Talbot's method, wet plates are cumbersome and have to be developed immediately after they are exposed.
• 1859: Celebrated British physicist James Clerk Maxwell (pictured, right) produces the first color photograph (of a tartan ribbon).
• 1871: Englishman Richard Maddox improves on Frederick Scott Archer's work by figuring out how to make photographs using dry plates and a gelatin emulsion. The method is quicker and allows photographs to be developed some time after exposure (instead of immediately).
• 1883: American George Eastman revolutionizes photography by inventing inexpensive, plastic photographic film.
• 1889: George Eastman makes it possible for millions of people to take up photography by launching his simple, inexpensive Kodak camera with the marketing line: "You Press the Button, We Do the Rest."
• 1896: German Wilhelm Röntgen takes the first X ray photograph (of his wife's hand).
• 1924: The German Leica company begins selling the 35mm photographic film that soon becomes a worldwide standard.
• 1931: Harold Edgerton invents the xenon-strobe flash lamp, making possible photography of objects moving at high speed.
• 1930s: Inexpensive Kodak and Agfa color film becomes available.
• 1947: American physicist Edwin Land invents a camera that can produce instant photographs, named the Polaroid Land Camera.
• 1963: Edwin Land releases an improved, color version of his Polaroid camera.
• 1985: Cameras appear with DX coding, a barcode system that allows the camera to read the film speed (and number of frames) automatically from the film container and adjust itself automatically.
• 1990s: Inexpensive digital cameras begin to make film obsolete. Some photographers stick with the old technology, but many stores stop selling film altogether.
• 2008: Polaroid company stops manufacturing instant film due to lack of demand.

Photo: Right: If you'd been a keen amateur photographer in the 1930s, you might have used a compact camera like this Soho Cadet (made in London, England), which packs into a sturdy outer case made from tough Bakelite plastic. The front of the case hinges down to reveal the camera mechanism inside. You pull on the lens and it extends out from the case on a leather bellows. You can focus the camera very crudely by pulling the bellows out from the case slightly more or slightly less, so adjusting the distance between the lens and the film. You can also crudely adjust the exposure with a slider control just above the lens. You can just make out the little viewfinder on the top right of the lens (as we look at it). You'll find a bigger version of this photo, with notes, on our Flickr.

Further reading

On this website

You might like these other articles on our site covering similar topics:

• CCDs (charge-coupled devices)
• Digital cameras
• Light

General

• Photography: Wikipedia has a good background overview and lots of shorter articles linked off it.

Museums

• The Niépce House Museum: The building in France where the first photo was taken.
• Lacock Abbey, Fox Talbot Museum and Village: The home of William Henry Fox Talbot in England.
• George Eastman House: An international museum of photography in Rochester, New York.
• International Center of Photography: A museum in New York City.
• The National Media Museum UK: A museum of photography, film, television, radio, and similar culture, based in Bradford, England.
• American Museum of Photography: An online photography museum!
• US Library of Congress: Daguerreotypes Portraits and Views: The LoC has a collection of over 725 daguerreotypes dating from the mid-19th century, many of which can be viewed online.

Books

• The New Manual of Photography by John Hedgecoe: A classic introductory book covering all aspects of photography.
• Digital Photographer's Handbook by Tom Ang: An introduction to digital techniques.
• Digital Photography All-in-One Desk Reference For Dummies: A 752-page simple introduction to digital cameras and photography.
• A World History of Photography by Naomi Rosenblum. Another classic work, this time covering photography's impact on society and culture.